The European Telecommunications Standardisation Institute (ETSI) is currently in the process of standardising a new set of protocols for third generation mobile telecommunications systems. The set of protocols is known collectively as Universal Mobile Telecommunications System (UMTS). FIG. 1 illustrates schematically the logical architecture approach of UMTS, where UE 1 designates User Equipment, BS 2 designates a Base Station, RNC 3 designates a Radio Network Controller, MSC 4 designates a Mobile Switching Centre, and SGSN designates a Serving GPRS Support Node (the MSC and SGSN are illustrated in FIG. 1 by a single entity but in practice are distinct nodes forming parts of respective core networks). The BS 2 and the RNC 3 form part of the UMTS Terrestrial Radio Access Network (UTRAN) 5. The illustrated architecture can be divided into two planes; a non-access plane which contains logical elements, and an access plane which contains all of the radio access and radio specific functionality.
The non-access plane includes an end-user (end-to-end) service 6. This is the logical connection between the UE 1 and an external user 15 (connected to an external network, e.g. PSTN, Internet, etc) using an external transport function 7. A UMTS service 8 uses a transport service 9 between the MSC 4 and the external core networks and services provided by the UTRAN.
The access plane includes the logical functionality and services represented by the blocks 10 to 14. The UMTS Radio Access Bearer (RAB) service 10 provides a transport connection service through the UTRAN, which uses Asynchronous Transfer Mode (ATM) through the blocks 11 and 12. WCDMA radio traffic channels 13 are allocated by the controllers in the RNC 3 and are physically implemented by the BS 2 over the radio interface to the UE 1. Block 14 represents the actual radio link resources which in a WCDMA system correspond to individual CDMA spreading codes.
In order to initiate a RAB service, a request for communication with a UE 1 is transmitted from the core network to the UTRAN 5. One or more parameters accompany the RAB service request. When establishing a RAB, the UTRAN flexibly maps or allocates the RAB to physical transport 11,12 and radio channel 14 resources through the UTRAN 5 and over the air interface respectively. The mapping is based upon one or more of the parameters associated with the RAB service request. During a connection, the UTRAN may change the radio resources allocated to a RAB in order to optimise the total usage of resources in UTRAN with respect to interference levels, capacity, coverage, etc. The core network is not informed about such changes in the allocated radio resources so long as the connection remains within the “service contract” defined at RAB establishment.
Two types of radio channels 14 are defined in UMTS. A “dedicated” channel (dch) exists where a CDMA spreading code is allocated to a single MS, whilst a “common” channel (cch) exists when the resources afforded by a spreading code are divided amongst two or more MSs. The choice of whether to allocate a common channel or a dedicated channel to a given RAB is made by a Radio Resource Controller of the serving RNC 3, and depends upon the actual data transfer requirements of the MS 1. The allocation is dynamic in so far as switching between common and dedicated channels may occur for a given RAB during a connection, as the level of data to be transferred varies. UTRAN radio resource handling may therefore change the radio resources allocated to a RAB by switching between common and dedicated channels, or by changing the allowed data rate on dedicated channels.